The present invention generally relates to actuator circuits and more particularly relates to electrically actuated actuator with two connections, with such an actuator preferably being an electromechanically actuated device having a solenoid, a coil or similar element.
In particular, actuators for safety-critical applications are commonly used in vehicles. An electronically controlled brake force booster is such an actuator. Like a conventional brake force booster, it comprises the actual, pneumatically driven boosting element which, however, is not driven directly mechanically when the brake pedal is pushed down, but through an electrically actuated valve that either ventilates or does not ventilate the vacuum side according to electric signals. Hence, the operation of the electrically actuated ventilation valve directly affects the brake reaction of the vehicle, so that, on the one hand, it is desired that this ventilation valve or actuator always works perfectly and, on the other hand, it must be ensured that testing such an actuator does not lead to undesired actuations of the brake system of a vehicle.
DE-OS 44 25 578 provides a schematic representation of a brake system with an electrically controlled brake force booster. However, it does not state how the components of the electric activation of the valve can be tested reliably on the one hand, and uncritically as far as the brake reaction of the vehicle is concerned on the other hand.
The object of the present invention is to disclose a circuit arrangement for an actuator or a method for testing the circuit arrangement of an actuator, on the basis of which the electric or electronic components can be tested simply, reliably and uncritically as far as the brake reaction of the vehicle is concerned.
Prior to describing individual embodiments of the invention, possible faults are described on the basis of FIG. 1. In FIG. 1 reference number 100 is the actuator under review or its electric components, in particular, for example, a solenoid, a coil, an electric motor or similar element. The actuator has two connections 100a and 100b. This actuator can be connected between potentials 101, 102 by means of its connections 100a, 100b. For example, 102 can be ground, 101 can be the battery supply voltage (usually 12V) or another suitable voltage. In conventional systems the operation of actuator 100 is controlled by means of a switch: The actuator works when the switch is closed and it rests when the switch is open. Various faults may occur as follows.
The switch may have a short-circuit or it may not close anymore. One of the connections 100a, 100b of actuator 100 may have a short-circuit with respect to one of the potentials 101, 102. Actuator 100 has an internal break or short-circuit. Finally, leakage currents towards the above-mentioned potentials may occur through high-resistance parallel connections. Most of the above-mentioned faults will immediately affect the performance of the actuator and should be detected as soon as possible in order to avoid insecure operating states.
Thus, a circuit arrangement that allows frequent testing of the actuator is desired. On the one hand, such testing, in particular, should be possible when the actuator could be potentially used, in other words while a vehicle is driving. On the other hand, it must be ensured that the testing does not lead to undesired intervention, e.g. undesired brake actuation.
Accordingly, the present invention discloses a circuit arrangement comprising two electronically actuated switches on each of the connections of the actuator. When activating the actuator in the conventional way, one of the switches can be closed firmly and another switch can be activated in accordance with other control criteria. During testing operations one switch can remain open and another can be closed, so that faults can be detected through the potential states.